It has been suggested that a visual analysis of the graphical output of a spectrum recording machine can be used to determine the presence or absence of pathological stenosis. More particularly, it has been suggested that waves can be directed toward a blood vessel, that a spectrum recording machine can be used to develop a graphical output representing the resulting plural-frequency response, and that a visual analysis can be made of that portion of that graphical output which is in the five kilohertz to twelve kilohertz range to determine the presence or absence of pathological stenosis. However, the use of visual analyses of the graphical outputs of spectrum recording machines is slow, indirect, expensive and difficult. It has also been suggested that sounds which are developed by a continuous wave, directional Doppler Flow Meter can be sensed aurally to determine the presence or absence of pathological stenosis. However, some difficulties have been experienced in using such sounds to make such determinations.